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Phys Rev Lett. 2014 Jul 11;113(2):026803. Epub 2014 Jul 10.

Tightly bound excitons in monolayer WSe(2).

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Department of Physics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, Ohio 44106, USA.
Department of Physics and Astronomy, The University of Kansas, Lawrence, Kansas 66045, USA.
Kavli Institute at Cornell for Nanoscale Science and Laboratory of Atomic and Solid State Physics, Cornell University, Ithaca, New York 14853, USA.


Exciton binding energy and excited states in monolayers of tungsten diselenide (WSe(2)) are investigated using the combined linear absorption and two-photon photoluminescence excitation spectroscopy. The exciton binding energy is determined to be 0.37 eV, which is about an order of magnitude larger than that in III-V semiconductor quantum wells and renders the exciton excited states observable even at room temperature. The exciton excitation spectrum with both experimentally determined one- and two-photon active states is distinct from the simple two-dimensional (2D) hydrogenic model. This result reveals significantly reduced and nonlocal dielectric screening of Coulomb interactions in 2D semiconductors. The observed large exciton binding energy will also have a significant impact on next-generation photonics and optoelectronics applications based on 2D atomic crystals.

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